1. Field of the Invention
The present invention relates to a zoom lens. The present invention also relates to an image pickup apparatus equipped with a zoom lens.
2. Description of the Related Art
There is a conventionally known small-size zoom lens for use in a digital camera that has three or more lens units including a lens unit having a negative refracting power disposed closest to the object side, a lens unit having a positive refracting power disposed closest to the image side, and an intermediate lens unit having a positive refracting power disposed therebetween, as disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2001-343587 and 2005-338344.
Disposing a lens unit having a negative refracting power closest to the object side in the zoom lens of this type is advantageous in achieving an adequately large angle of field at the wide angle end zoom position and in reducing the size of the zoom lens with respect to the diametrical direction. In addition, disposing a lens unit having a positive refracting power closest to the image side facilitates locating the exit pupil farther from the image plane and reducing color shading.
In this zoom lens, the intermediate lens unit is moved during zooming in such a way that it is located closer to the object side at the telephoto end than at the wide angle end, and the lens unit closest to the image side is moved in such a way that it is located closer to the image side at the telephoto end than at the wide angle end. By moving the lens unit in this way, the magnifying effect is shared by the intermediate lens unit and the lens unit closest to the image side, which is advantageous in achieving an adequate zoom ratio.
In addition, an aperture stop is moved integrally with the intermediate zoom lens, which facilitates a reduction in the size of the intermediate lens unit and simplification of a driving mechanism for zooming.